The prior art, in particular Offenlegungsschrift DE 10 2004 018 146 A1, discloses a method and an apparatus for blow molding containers, in the case of which preforms consisting of a thermoplastic material are first heated to the right temperature within a blow mold and are then, on the one hand, stretched by a stretch rod, and, on the other hand, inflated into containers by supplying compressed air into the interior of the preform. The compressed air is supplied though the stretch rod. In addition, said publication mentions the possibility of discharging compressed gas from the shaped container through the stretch rod and of achieving, in so doing, an additional cooling effect by predetermining suitable flow directions.
In the case of the cited prior art, the material yield is often insufficient in the contact area of the stretch rod tip and of the preform. When high requirements on the container quality and the material yield are to be met, it will, however, be necessary to stretch the material also in this contact area.